1. Field of the Invention
The invention relates to a method of producing a joined article of a semiconductor wafer supporting member, and a joined article of a semiconductor wafer supporting member.
2. Related Art Statement
In a semiconductor processing such as CVD, sputtering and etching, a semiconductor wafer is mounted on a susceptor, which is then heated to carry out the heat treatment of the wafer. Japanese patent laid-open publication 124, 140A/1984 disclosed the following process. An electrostatic chuck made of a ceramic material is used as a susceptor for adsorbing a semiconductor wafer and is heated to subject the wafer to a heat treatment. Alternatively, a ceramic heater is used as susceptor for mounting a semiconductor wafer thereon and involves directly heating the wafer. It is, however, necessary to reduce the temperature change during the adsorption-desorption cycles of semiconductor wafers on a susceptor to further improve the production of the semiconductor wafers. It is therefore needed to control and switch the heating and cooling of the wafer with a reduced time delay. The necessity of controlling the heating-cooling cycle demands a cooling system connected with the susceptor.
A technique of joining an electrostatic chuck onto a metal cooling board of the water cooling type by means of metal bonding was proposed by (Japanese Patent laid-open (Kokai) Publication A3249/1991). According to this technique, an electrostatic chuck with an alumina substrate and a water cooling board made of aluminum are joined by metal bonding using indium metal.
When indium is used as an adhesive for joining a ceramic electrostatic chuck and a water cooling flange made of a metal, however, an insufficient pressure during the joining process may induce bonding defects in the joining layer. The defects may reduce the reliability of the air-tightness of the joining layer. If the air-tightness along the joining interface of the electrostatic chuck and cooling flange would be insufficient, there would be a risk that a corrosive gas in a chamber might be leaked along the joining interface from the chamber. Moreover, when a back side gas is supplied between the back face of the semiconductor wafer and the chuck, there would be a risk that the gas might be leaked along the joining interface of the chuck and cooling flange. It is therefore demanded to secure the air-tightness along the joining interface between the chuck and flange with an excellent reliability.
Further, the flatness of the adsorption face for the wafer of the chuck may be deteriorated after the joining process, due to the difference of the thermal expansion between the ceramic chuck and metal flange. A specified flatness is demanded for the adsorption face of the chuck for adsorbing the wafer during semiconductor processing. The chuck having the deteriorated flatness may thus be an off-specification product and reduces the production yield of the ceramic chuck.
An object of the invention is to provide a novel joined article having a ceramic supporting member for a semiconductor wafer, a metal member and a joining layer joining the supporting and metal members, and to improve the reliability of the air-tightness along the joining interface between the supporting and metal members. Another object of the invention is to prevent the deterioration of the flatness of the supporting face of the supporting member after the joining process.
The present invention provides a method for producing a joined body comprising a supporting member made of a ceramic material for supporting a semiconductor wafer, a metal member and a joining layer for joining the supporting and metal members. The method comprises the steps of:
forming a first metal film on a surface to be joined of the supporting member;
forming a second metal film on a surface to be joined of the metal member;
placing a metal adhesive between the first and second films to provide an assembly; and
heating the assembly at a temperature not higher than a melting point of the metal adhesive while the assembly is subjected to isostatic pressing so that the supporting and metal members are joined by diffusion joining.
The invention further provides a joined article obtained by the above method.
The inventors tried the following process. An assembly was prepared having a semiconductor supporting ember with a first metal film, a metal member with a second metal film and a metal adhesive. The assembly was heated at a temperature not higher than a melting point of the metal adhesive, while the assembly was subjected to isostatic pressing. They have found that the metal adhesive may be diffusion joined with the first and second films to provide a joined article of the metal and supporting members, and have thus attained the present invention. According to the present invention, it is possible to secure the air-tightness of the joining interface with improved reliability and to prevent the deterioration of the flatness of the supporting face of the supporting member after the joining process.
These and other objects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art.